Block copolymers of polydiorganosiloxane and polycarbonate in the form of film or sheet or as a layer from solution have been used in laminates particularly in conjunction with polycarbonate laminae. These block copolymers not only act as an adhesive interlayer joining two laminae but in effect enter into and enhance the laminate structure as a lamina, providing improved strength and ductility over an extremely wide range of temperatures. These physical characteristics, accompanied over a wide range of temperatures by salutary weather resistance and optical clarity, make laminates containing laminae of these block copolymers particularly useful in so-called safety glazing applications where resistance to penetration and spalling from the impact of flying objects such as bullets, rocks, missiles, and the like is desirable.
As with all laminates, the stability and useability of laminates containing polydiorganosiloxane-polycarbonate block copolymer laminae depend upon a variety of intrinsic and extrinsic factors. These factors include adhesion, residual stresses, processing parameters, and the environment in which they are used.
With respect to adhesion, a variety of methods for cleaning or activating the surface of laminae before consolidating the laminate have been used. For example, such methods may employ chemical priming agents, a corona treatment, and others.
The level of the art is now such that depending on the composition of the adhesive interlayer, specific surface treatments are recommended for cleaning, priming, or activating the surface of thermoplastic laminae such as laminae of polycarbonate, polyacrylate, or polystyrene. Rules of thumb and general bonding principles no longer provide the most desirable surface treatment methods nor the best adhesion in a growing number of specific instances.
U.S. Pat. No. 4,169,181 assigned to the same assignee as the present invention discloses an impact resistant laminate having amongst its laminae an adhesive interlayer of a polydiorganosiloxane-polycarbonate block copolymer adhered to a lamina of polycarbonate. The bonding process does not include the use of a primer composition or special surface treatment. Thus, the level of adhesion between the polydiorganosiloxane-polycarbonate block copolymer and polycarbonate laminae is nonuniform across the surface of the bond sometimes resulting in delamination.
U.S. Pat. Nos. 4,027,072 and 4,040,882 assigned to the same assignee as the present invention discloses laminates containing laminae of polysiloxane-polycarbonate block copolymer adhered to a lamina of glass or polycarbonate. In order to enhance the adhesion of the polydiorganosiloxane-polycarbonate block copolymer to the glass or polycarbonate the glass or polycarbonate surface is primed with a solution containing alpha-amino propyltriethyoxysilane before consolidation of the laminate. Adhesion is improved by the application of the primer but even greater adhesion is desirable.
U.S. Pat. No. 4,204,026 assigned to the same assignee as the present invention discloses a laminate having an aminoalkyl [poly(aryloxysiloxane)] primer deposited on a lamina of glass to which an adhesive interlayer of polydiorganosiloxane-polycarbonate block copolymer is adhered. This primer is to enhance the adhesion of the polydiorganosiloxane-polycarbonate block copolymer to glass. This primer is not disclosed as suitable to enhance the adhesion of a polydiorganosiloxane-polycarbonate block copolymer laminae to a polycarbonate laminae.
U.S. Pat. No. 3,666,614 discloses the use of a primer composition containing a silane and a solvent system to increase adhesion between an ethylene-vinyl acetate copolymer adhesive interlayer and polycarbonate or glass. Further, U.S. Pat. No. 4,126,730 assigned to the same assignee as the present invention discloses this primer to be suitable for use as an adhesion promoter between a polydiorganosiloxane-polycarbonate block copolymer lamina and a polycarbonate lamina. The silanes are preferred for use where one of the lamina to be bonded is glass.
Thus, while laminae of polydiorganosiloxane-polycarbonate block copolymers are frequently bonded with satisfactory results to thermoplastic laminae and polycarbonate, there exists a need for a primer composition to increase the adhesion between the two laminae and to increase the uniformity of the resulting bond strength across the face of the bond. Furthermore, while such primers have been proposed in the past, none has proven completely satisfactory in increasing the strength and consistency of adhesion of polydiorganosiloxane-polycarbonate block copolymer laminae to thermoplastic laminae and particularly to laminae of polycarbonate.
Therefore, it is an object of the present invention to increase the adherence of a polydiorganosiloxane-polycarbonate block copolymer lamina or adhesive interlayer to an adjoining thermoplastic lamina or layer.
It is another object of the present invention to provide a method for bonding a polydiorganosiloxane-polycarbonate block copolymer lamina or layer to a thermoplastic lamina or layer and thereby produce a laminate or multi-ply composite of at least two plies.